Studies suggest that activation of P2Y receptors and/or P2X receptors by extracellular nucleotides (such as ATP and UTP) elicit responses from inflammatory cells (such as mast cells, eosinophil, leukocytes, neutrophils) consistent with a pro-inflammatory effect. ATP is required to stimulate histamine release from rat peritoneal mast cells and histamine and prostaglandin D2 in rat serosal mast cells (Jaffar and Pearce, Agents Actions 30(1-2): 64-6 (1990); Izushi and Tasaka, Pharmacology 42(6): 297-308 (1991)). In the latter case, the effects of ATP were inhibited by reactive blue 2 and suramin, two putative antagonists for P2Y receptors. Anti-IgE-induced histamine release from human lung mast cells was significantly enhanced by ATP and UTP at low concentrations (10−6 to 10−4 M) but inhibited at high concentrations (10−3 M), indicating a bimodal action (Schulman, et al., Am. J. Respir. Cell. Mol. Biol. 20(3):530-7(1999)). Adenine and uridine nucleotides (ADP, ATP, and UTP) activate chemotaxic signals on cultured rat bone marrow mast cells and may function to recruit mast cells by intestinal mucosa as part of a parasitic response (Saito, et al., Int. Arch. Allergy Appl. Immunol. 94(1-4): 68-70 (1991); McCloskey, et al., J. Immunol. 163(2): 970-7 (1999)).
Purinergic receptors, via the action of ATP and UTP, were also shown to be involved in nucleotide responses of human neutrophils in mediating an enhanced O2 response to the chemotactic peptide N′-formyl-Met-Leu-Phe (Walker, et al., Lab Invest. 64(1): 105-12 (1991)). For example, short incubations of polymorphonuclear leukocyte (PMN) with ATP and UTP enhanced the oxidative burst induced by N′-formyl-Met-Leu-Phe. In human neutrophils, ATP was shown to stimulate the elevation of cytosolic free calcium concentration via the action of a P2 receptor (Merritt and Moores, Cell Signal 3(3):243-9 (1991); Walker, et al., Lab Invest. 64(1): 105-12.et al. (1991)).
Extracellular nucleotide-induced stimulation of leukocytes and subsequent adhesion to endothelium has been shown to play an important role in inflammatory diseases. Extracellular nucleotides stimulate P2Y receptor on human polymorphonuclear neutrophils (PMN) with the pharmacological profile of the P2Y2 receptor. It is postulated that extracellular nucleotides require leukotriene generation as an essential intermediate for mediating neutrophil degranulation (Kannan, Med. Hypotheses 57(3): 306-9 (2001)).
Extracellular nucleotides also elicit multiple responses in eosinophils, which have been shown to express various P2X and P2Y subtypes (Ferrari, et al., FEBS Lett. 486(3): 217-24 (2000)). For example, ATP was shown in human eosinophils to stimulate cytosolic calcium levels, production of reactive oxygen species, and upregulation of the pro-inflammatory marker integrin CD11b (Dichmann, et al., Blood 95(3): 973-8 (2000)). In addition to such actions, P2Y agonists have also been shown to increase intracellular Ca++ due to stimulation of phospholipase C by the P2Y2 receptor (Brown, et al., Mol. Pharmacol. 40, 648-655 (1991); Yerxa and Johnson, Drugs of the Future 24(7): 759-769 (1999)). ATP is a strong activator of eosinophils, with biological activity comparable to those of other known neutrophilic chemotaxins, thereby strongly suggesting a role of P2 receptors as activators of pro-inflammatory effector functions (Dichmann, et al. , Blood 95(3): 973-8 (2000); Mohanty, et al., J. Allergy Clin. Immunol. 107(5): 849-55 (2001)).
The preponderance of observations suggests that activation of P2Y receptors and/or P2X receptors by extracellular nucleotides such as ATP and UTP elicit responses from inflammatory cells (such as mast cells, eosinophil, leukocytes, neutrophils) consistent with a pro-inflammatory effect. Thus these findings suggest a role of P2Y receptor agonists in increasing inflammatory effects.
Purinergic receptor agonists have been disclosed in the following patents. U.S. Pat. Nos. 5,789,391; 5,763,447; 5,635,160; 5,935,555; 5,656,256; 5,628,984; 5,902,567; 5,292,498; 5,837,861; 5,900,407; 5,972,904; 5,981,506; 5,958,897; 5,968,913; 6,022,527; 6,133,247; and 6,143,279, and PCT publications WO97/29756, WO97/35591, WO96/40059, WO97/05195, WO94/08593, WO98/19685, WO98/15835, WO98/03182, WO98/03177, WO98/34942, WO98/34593, WO99/09998, WO99/32085, WO99/61012, WO 00/30629, WO 00/50024, and WO 96/40059 disclose methods of treating sinusitis, otitis media, ciliary dyskinesia, pneumonia associated with immobilization, lung disease, cystic fibrosis, dry eye disease, vaginal dryness, bronchitis, edematous retinal disorders, retinal degeneration and detachment, and gastrointestinal disease, by administrating dinucleoside polyphosphates and related compounds to a patient.
The search for compounds that counteract or inhibit inflammatory effects is still an area of active research. It would be very desirable to find new compounds with this ability, particularly if these compounds were to function via unknown pathways.